The liquid crystal display panel is a display panel which controls alignment of a birefringent liquid crystal molecule to control transmission/shielding (ON/OFF in display) of light. The liquid crystal display panel generally includes a color filter for color display and a polarizer which transmits only a specific polarization component of incident light. According to such a liquid crystal display panel, it is commonly known that an anti-reflective film for reducing a reflectance by light interference is arranged on a surface of a display (display screen) as means for preventing reflection of external light. FIG. 8 is a cross-sectional view showing an arrangement configuration of an anti-reflective film which reduces a reflectance by light interference. As shown in FIG. 8, such a type of an anti-reflective film 23 is arranged on an observation side surface of a base material 22 arranged on a display 21. The configuration of this type of the anti-reflective film is designed in such a way that incident light 24 is divided into two reflected lights 24a and 24b, and a phase of the reflected light 24a that has been reflected on the outermost surface of the anti-reflective film 23 is different from a phase of the reflected light 24b that has been reflected on the boundary surface between the anti-reflective film 23 and the base material 22 just by N-½ (N is an integer of 1 or more). Accordingly, the phase of the reflected light 24a is opposite to the phase of the reflected light 24b. Therefore, the phases cancel each other by interference. Using this, the reflectance can be reduced.
Conditions for reducing a reflectance of the anti-reflective film depend on a wavelength of light to be reflected. FIG. 9 is a graph showing a reflection spectrum of a common anti-reflective film. As shown in FIG. 9, the reflection spectrum of the common anti-reflective film is shown by a U shape having the bottom at a specific wavelength. In FIG. 9, the reflection spectrum is an integrating sphere reflectance measured using a spectrophotometer (product of Hitachi High-Technologies Corporation, trade name: U-4100).
As shown in FIG. 9, it is difficult for the conventional anti-reflective film to reduce the reflectance uniformly in the entire wavelength region. Under such a circumstance, in view of neutral color (achromatic color) in chromaticity of reflected light and luminous reflectance (Y value), an anti-reflective film which is designed in such a way that the bottom wavelength of the reflectance is 550 to 600 nm is known. Herein, the luminous reflectance means tristimulus values Y obtained from a reflection spectrum of light reflected by the anti-reflective film, a spectrum of light outputted from a standard light source, and color matching functions corresponding to sensitivity of a human eye.
If the display surface is touched by a bare hand and thereby a fingerprint adheres to the anti-reflective film, for example, the optical design is changed at the part where the fingerprint has adhered. As a result, the part where the fingerprint has adhered is tinted. Even if the fingerprint is wiped off, the fingerprint is not completely removed and the sebum tends to remain, generally. In such a case, the remained sebum is tinted to shin. In this point, the anti-reflective film has room for improvement in order to prevent a reduction in display qualities even in the case that stains such as a fingerprint adheres to the surface of the anti-reflective film.
For this problem, it is disclosed that an anti-reflective film surface is coated with a hydrophobic anti-stain film, thereby preventing stains such as a fingerprint and a water stain from adhering to the anti-reflective film surface. Further, it is disclosed that an anti-reflective film is subjected to multi-coating of thin films to have some different bottom wavelengths in a visible light region, thereby preventing reflected light from being tinted (for example, refer to Patent Document 1). However, a method capable of more easily preventing the reduction in display qualities, caused by stains such as a fingerprint, has been desired.
With regard to the wavelength where the reflectance of light reflected through the anti-reflective film is minimum, it has been known that, in a projection type display device, an anti-reflective film whose bottom wavelength has been adjusted is arranged on a surface of a polarizer, in order to prevent return light from an output side from entering a TFT (thin film transistor) liquid crystal panel, thereby preventing a reduction in image qualities due to an increase in leakage current, or alternatively in order to suppress an increase in reflectance of red at any incident angle of a light beam in CRT (a cathode-ray tube) display (for example, refer to Patent Documents 2 and 3). However, Patent Documents 2 and 3 neither disclose nor suggest a method of preventing the reduction in display qualities when stains such as a fingerprint adhere to the anti-reflective film.
[Patent Document 1]
Japanese Kokai Publication No. Hei-07-5452
[Patent Document 2]
Japanese Kokai Publication No. Hei-09-96805
[Patent Document 3]
Japanese Kokai Publication No. Hei-11-204065